You could also build up a temporary pseudo-account based on an anonymous user's session that could optionally be upgraded to a permanent account with an ID and password at any time.
This is common with e-commerce sites. Many don't require you to make an account to add items to your shopping cart or even to check out. But if you want to make an account, they make it super easy prefilling info they already have, and they certainly won't make you lose what's in your cart.
This is common with e-commerce sites. Many don't require you to make an account to add items to your shopping cart or even to check out. But if you want to make an account, they make it super easy prefilling info they already have, and they certainly won't make you lose what's in your cart.